Hah! I'm doing a terrible job of explaining this.
(Sorry, Mr. Lucas...) Take the Star Wars prequels and compare them to the originals and Episode: VII. The prequels are largely garbage, both in story arc, writing, and execution. My favorite comparison:
Padme: (Intimately.) "I truly...deeply...love you. And before we die, I want you to know."
Anakin: (Silent, intense stare into her eyes.)
vs.
Leia: (Frantically.) "I love you."
Han: "I know."
Even though Han-and-Leia was technically ad-lib, it made its way into the final script -- and it's brilliant. It's two unique characters, completely in-the-moment, responding to that moment in ways that only those two characters could speak. The subtext reflects volumes about their unique relationship, which is drowning in conflict. She would never open up to him. She would never let her guard down. She had to be a strong leader, keeping her personal feelings in check for the good of her cause. He, on the other hand, knew how to read her, which was why he played it cool but never missed an opportunity to dig at her defenses. Now, they're about to be torn apart, perhaps for good. She blurts it out at literally the last second...and he responds with two words that capture the arrogance of his character at the same time as they reassure her that her feelings weren't wasted on him. Complete, cinematic brilliance.
Padme-and-Anakin sounds like every sappy exchange between two characters written by every untrained writer I've ever come across. Where's the moment? Where's the unique exchange of these two characters' love that belongs only to them? We refer to this stuff as "throw-away" dialogue -- words used simply to blow by a scene we don't really care that much about (usually because we're pressed for time and finishing the script is a matter of triage). I'll completely cut it if I can. If not, I'll try to find some way of mitigating its ho-hum effect. I'll be darned up in paisley before I refer to that type of writing as quality, though. Even if I'm the one writing it in.
This is my overall issue with the companion banter as it stands. (And not all of it! Only some of the throw-away comments.) Hearing it once is ho-hum. Hearing it over and over can grate.
Bethesda employs some pretty fantastic voice actors as well. There's only so much you can do with clunky lines or a clunky scene, though. That's where quality writers, unknown and under-appreciated in the extreme, really get to shine. Bioware produces real meat for their actors to chew. Sera in DA:I is one of my favorite scripts. Especially the -- "Having someone like you around is like...having these great, big, huge ears...! Shut up!" -- moment; I laughed out-loud at that!
Good writing is universal. It doesn't apply only to one medium, nor does quality differ between genres. If any game, film, novel, short story, cartoon, etc. is going to include characters, those characters deserve to be well-written. Bioware has definitely set a standard with this aspect, plus they budget their games to include the writers' and actors' salaries.
Despite this aspect being far superior to Bethesda games...I still like playing Bethesda games more. It's definitely not everything! I'd like to see Beth make strides, though.